1. Field of the Invention
The invention relates generally to electroplating apparatus, and more specifically to a clamp for securing and electrically connecting an object to be electroplated to an electroplating rack for immersion in an electroplating solution.
2. Prior Art
In the inventor's prior U.S. Pat. No. 4,176,039, an electroplating rack is disclosed utilizing a clamp having a clamp screw and an opposing clamp pad, both the clamp screw and clamp having a structure which provides the appropriate clamping forces and electrical connections to an object to be electroplated, while establishing seals for isolating the electrically conductive elements of the clamp from the plating solution. As will be further discussed in connection with prior art FIGS. 1 and 2, the present invention is an improvement over the structure of the clamp disclosed in the inventor's U.S. Pat. No. 4,176,039 patent as shown in FIG. 2A and the structure of the clamp developed by the inventor as shown in FIG. 2B. The clamp developed by the inventor as shown in FIG. 2B includes a clamp screw, the shank of which has a threaded electrically conductive central portion and electrically insulating unthreaded portions which are contiguously joined to the front and rear of the conductive portion. The central conductive threaded portion of the shank engages a central metallic portion of a threaded opening in the clamp frame and makes electrical contact therewith. The forwardly extended unthreaded shank portion of the clamp screw engages another non-metallic (insulating) threaded portion of the opening of the clamp frame, with the distal end of the conductive screw portion being exposed for electrically and mechanically contacting the clamp workpiece. The rearwardly extended unthreaded shank portion of the clamp screw extends axially between the central metallic conductive threaded portion and the handle of the clamp; this portion engages another non-metallic (insulating) threaded portion of the opening of the clamp frame. Since the frame is covered with insulating material, the only electrical contact between the object to be plated and the frame is through the clamp screw and opposing clamp pad. The central portion of the clamp screw is electrically accessible--the end portions of the screw as aforementioned are covered with insulating material, which is to shield the screw's metal skeleton from plate build-up and chemical attack of solution, while simultaneously isolating the engaged central metallic threaded portion from the plating solution to also prevent jamming from plate build-up and reduced chemical attack thereof.
The aforementioned clamp screw was found, however, not to provide as satisfactory a sealing action as desired because the threads in both the forward and rearward portions 8c and 8a, respectively, of the clamp frame were unfilled by the unthreaded portions 7a and 7c of the clamp screw--compression notwithstanding. A pathway for the plating solution to enter the system was thereby provided; and, as a result, plate build-up occurred on both the electrically conductive threaded portion 7b of the clamp screw and the electrically conductive threaded opening 19 in the clamp frame.
The clamp disclosed in the inventor's U.S. Pat. No. 4,176,039 and as shown in FIG. 2A includes a clamp screw, the threaded shank of which, while including a conductive core, is externally of a tripartite construction. In particular, the axially extending shank of this prior art screw includes a threaded electrically conductive central portion and resilient, electrically insulating threaded portions which are contiguously adjoined to the front and rear of the said conductive portion. The central conductive threaded portion of the shank engages a central metallic portion of a threaded opening in the clamp frame and makes electrical contact therewith. The forward threaded shank portion (of insulating material) engages another non-metallic (insulating) portion of a threaded opening of the clamp frame, with the distal end of the conductive core being exposed for electrically and mechanically contacting the clamped workpiece. The rearwardly extending threaded portion (of insulating material) extends axially between the central metallic conductive threaded portion and the handle of the screw; this portion engages the other non-metallic insulating portion of the threaded opening of the clamp frame. Since the frame is covered with insulating material, the only electrical contact between the object to be plated and the frame is through the threaded screw, the central portion of which is electrically accessible--the end threaded portions of the screw as aforementioned are covered with insulating material, which shields the screw's metal skeleton from plate build-up and chemical attack of solution, while simultaneously isolating the engaged central metallic threaded portion from the plating solution to also prevent jamming from plate build-up and reduce chemical attack thereof.
The aforementioned tripartite screw is of subtle and precise construction, and while it is more efficacious in sealing the central threaded conductive portion from electrolyte than the one depicted in FIG. 2B, it is difficult and expensive to fabricate and repair.